To save some money on a summer vacation to Puerto Rico, Kim Gismervik decided to rent a house for her family instead of paying for multiple hotel rooms. After scouring the Web for the perfect place, she landed at Cyberrentals.com, where she found a three-bedroom villa on the north coast of the island with a grill, shared pool and back yard for $1,400 for the week.

But when the family arrived, they were sorely disappointed. The bed linens were stained and soiled, said Gismervik. The grill was old and rusted. There was mold in the refrigerator. And a loudly barking dog next door was not cleaned up after, causing the family to keep the first-floor windows shut tight to keep out the stench.

“We ended up leaving midweek, the conditions were so bad,” said Gismervik, a marketing director from Albany, N.Y. “We couldn’t take it anymore.”

The owner, she said, later apologized for the condition of the home, but did not provide any compensation. Moreover, Gismervik ended up paying an additional $2,000 to stay at a Marriott for the rest of the trip, and the experience soured her on vacation rentals. “I would not choose ever to do that again,” she said.

The Internet has made it ever easier for travelers to search for vacation rentals across the globe, but at the same time it has also made it possible for just about anyone with a spare room to post a listing. Faced with the soft real estate market, many homeowners do just that. Houses that otherwise might be sold, or kept for private use, are going up for rent instead, and second-home owners with little or no experience with tenants are suddenly absentee landlords.

So how do you avoid the pitfalls? First, figure out whom you want to rent from. The vacation rental market is divided into two basic segments: homes that are rented out directly by the owner and those run by a property management company.

Professionally managed rentals, like most of the properties featured on Zonder.com, forGetaway.com and PickPackGo.com, promise a certain level of quality control since the homeowner pays the management company to inspect the home, clean it and handle any issues that arise. But the extra security tends to come at a higher cost.

Property managers charge homeowners anywhere from 10 percent to 45 percent of the rental revenue for services and commission, according to Discover Vacation Homes, an association of property management companies. Some of that cost gets passed on to consumers. “There’s a middle man there, with property managers,” said Steve Hassett, who heads up forGetaway.com. “They have to make money off it. Some of that comes from the owner of the property and some from the renter, but both sides feel like it offers a lot of value.”

No such quality control exists with owner-rented properties, found on sites like Homeaway.com. and Vrbo.com., but what you gain is cost savings. Both parties must work out the details of the rental agreement themselves, from the cost to where to pick up the keys.

Regardless of whom you rent from, it’s a good idea to seek out recommendations from fellow renters. Vacation rental sites are increasingly offering customer reviews, making it easier to evaluate whether a property lives up to its description.

But how those reviews are handled varies widely. For example, Cyberrentals.com., which is owned by Homeaway, notifies owners of user reviews before they go up. This gives homeowners the opportunity to respond to unfair criticisms or to dispute false reviews posted by someone who did not stay there, the company said.

But some users say that negative reviews have been censored. Gismervik, the marketing director from Albany, said she tried several times to post a review of her Puerto Rico villa (including the yard full of dog feces next door). But Cyberrentals wouldn’t accept it, she said, and asked her to remove her mention of the neighbor’s dog since it wasn’t part of the property.

Yet even after she modified the complaint, the site wouldn’t post it, she said, adding, “They just refused.”

Brian Sharples, chief executive of Homeaway, said removal of a review was “extremely rare” and occurred only after the company had tangible proof that the renter unfairly maligned the owner. “We are more than willing to lose property owners from our site if they aren’t treating our customers fairly or their advertisements are misleading,” Sharples said.

After being unable to post on Cyberrentals, Gismervik turned to Vacation Rentals WatchDog (www.vrwd.org), which lets customers complain about vacation rentals. The site was founded last year by John Romano, who runs several vacation rental Web sites and frequently hears about unreturned security deposits and misleading ads.

Romano said he tried to verify each complaint to make sure it was really from a renter — and not a competing rental company — by e-mailing the property owner for a response and checking Internet Protocol addresses, which can offer clues as to where the e-mail message was sent from. Still, he said, “it’s mostly based on trust.”

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